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<h3 class="section" id="Traditional-miscellany-1"><span>10.3 Traditional miscellany<a class="copiable-link" href="#Traditional-miscellany-1"> &para;</a></span></h3>

<p>Here are some things to be aware of when using the traditional
preprocessor.
</p>
<ul class="itemize mark-bullet">
<li>Preprocessing directives are recognized only when their leading
&lsquo;<samp class="samp">#</samp>&rsquo; appears in the first column.  There can be no whitespace
between the beginning of the line and the &lsquo;<samp class="samp">#</samp>&rsquo;, but whitespace can
follow the &lsquo;<samp class="samp">#</samp>&rsquo;.

</li><li>A true traditional C preprocessor does not recognize &lsquo;<samp class="samp">#error</samp>&rsquo; or
&lsquo;<samp class="samp">#pragma</samp>&rsquo;, and may not recognize &lsquo;<samp class="samp">#elif</samp>&rsquo;.  CPP supports all
the directives in traditional mode that it supports in ISO mode,
including extensions, with the exception that the effects of
&lsquo;<samp class="samp">#pragma GCC poison</samp>&rsquo; are undefined.

</li><li>__STDC__ is not defined.

</li><li>If you use digraphs the behavior is undefined.

</li><li>If a line that looks like a directive appears within macro arguments,
the behavior is undefined.

</li></ul>

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